Bio-oil is an academic concept and research area focused on the production, characterization, and valorization of complex liquid mixtures derived from the thermochemical conversion of biomass. This field investigates processes such as fast pyrolysis and hydrothermal liquefaction, the intricate chemical composition and physical properties of the resulting bio-oils, and subsequent upgrading methods to improve their suitability for use as renewable fuels, chemicals, or materials. Its significance stems from its potential to transform abundant biomass resources into valuable energy carriers and biochemicals, thereby contributing to the development of a sustainable bioeconomy and reducing reliance on fossil fuels.